Structural Polysaccharides: Chitin vs Cellulose

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Questions and Answers

What is a chiral carbon?

  • Attached to four different atoms or groups (correct)
  • Attached to five different atoms or groups
  • Attached to two different atoms or groups
  • Attached to three different atoms or groups

Which term describes an object that cannot be superimposed on its mirror image?

  • Achiral
  • Chiral (correct)
  • Isomer
  • Symmetric

Which representation of biological molecules provides a 3-D view?

  • Ball and stick (correct)
  • V-Line notation
  • Fischer Projection formulas
  • Perspective formulas

What is the purpose of using glyceraldehyde as a reference compound?

<p>To designate D and L configurations (A)</p> Signup and view all the answers

How are compounds designated as D or L sugars?

<p>Based on the location of the hydroxy group on the penultimate carbon (D)</p> Signup and view all the answers

For aldo-sugars, which carbon receives the lowest possible number in priority?

<p>Carbonyl carbon (A)</p> Signup and view all the answers

What determines whether a monosaccharide is designated as a D sugar?

<p>Its configuration compared to D-glyceraldehyde (B)</p> Signup and view all the answers

In the context of molecules, what does 'chiral' specifically refer to?

<p>'Chiral' means non-superimposable on its mirror image (C)</p> Signup and view all the answers

'Priority increases as atomic number increases' is associated with which rule?

<p>&quot;Priority Rule #1&quot; (B)</p> Signup and view all the answers

'D' and 'L' designations are given based on the configuration compared to which compound?

<p>'D-Glyceraldehyde' (A)</p> Signup and view all the answers

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Study Notes

Starch and Cellulose

  • Starch is composed of 1-4 linkages of α glucose monomers.
  • Cellulose is composed of 1-4 linkages of β glucose monomers.

Chitin

  • Chitin is the major component of arthropod exoskeletons and fungal cell walls.
  • It is a linear homopolysaccharide composed of N-acetylglucosamine linked by β(1→4) glycosidic bonds.
  • Chitin exists in three arrangements: α-Chitin (all parallel), β-Chitin (antiparallel), and γ-Chitin (pairs of parallel sheets separated by single antiparallel sheets).
  • Chitin is used to make strong and flexible surgical threads that decompose after healing.

Heteropolysaccharides

  • Heteropolysaccharides are often made up of repeating disaccharide units.
  • The carbohydrate component of peptidoglycan is made up of a repeating disaccharide unit consisting of N-acetylglucosamine (NAG/GlcNAc) and N-acetylmuramic acid (NAM/Mur2Ac).

Cellulose Structure

  • Cellulose is rigid and water-insoluble due to its β(1→4) glycosidic linkage.
  • The β(1→4) glycosidic linkage allows cellulose to form long straight chains.
  • Cellulose chains associate with each other via extensive hydrogen bonding, forming cellulose microfibrils.
  • Cellulose is predominantly of plant origin, but also occurs in the outer mantles of tunicates/sea squirts.

Cellulose Function

  • The role of cellulose is to provide structural support and rigidity to plant cell walls.
  • The structure of cellulose is suited to its function due to its rigid and water-insoluble properties.

Carbohydrate Representations

  • Carbohydrates can be represented using ball and stick, perspective, and Fischer projection formulas.
  • Glyceraldehyde is a reference compound used to name other compounds based on their relative configuration.

Chirality

  • Chiral carbons are attached to four different atoms or groups.
  • An object that cannot be superimposed on its mirror image is also said to be chiral.
  • D and L designations are given based on the relative configuration of a compound compared to glyceraldehyde.

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